Microscopic Parasite Toxoplasma Gondii Linked to Personality Changes

Toxoplasmosis, an infection caused by the microscopic parasite Toxoplasma gondii, infects about 22.5% of Americans, aged 12 and older. Researchers tested participants for T. gondii and had them complete a personality questionnaire. Both men and women infected with T. gondii were more extroverted and less conscientious than non-infected participants.

The changes are thought to come from the parasite’s influence on brain chemicals. The scientists published their findings in the European Journal of Personality. Toxoplasma manipulates the behavior of its animal host by increasing the concentration of dopamine and changing the levels of certain hormones, states Jaroslav Flegr, of Charles University, Prague, in the Czech Republic.

Red arrows point to Toxoplasma gondii in a pig’s lung

Humans carry the parasite, but its life cycle must play out in cats and rodents. Infected mice and rats lose their fear of cats, increasing the chances that they will be eaten, allowing the parasite to enter the cat and spread through its feces.

In humans, T. gondii‘s effects are subtler. The infected population has a higher rate of traffic accidents and people with schizophrenia have higher rates of infection. In a new study, a pattern seems to have appeared in infected men. The longer they were infected, the less conscientious they were. This correlation supports the scientists’ hypothesis, that the personality changes are a direct result of the parasite.

T. gondii is contracted through exposure to undercooked contaminated meat, unwashed fruits or vegetables that stem from contaminated soil, and tainted cat litter. The rates of infection in France are much higher than in the USA. The parasite is the reason why pregnant women shouldn’t clean litter boxes because the parasite can do much more damage on fetal brains than in adults.